THE UPPER SILURIAN PERIOD. 131 



dus, fig. 75, B), which are doubtless the bony scales of some 

 fish resembling the modern Dog-fishes. As the above mentioned 

 remains belong to two distinct, and at the same time highly- 

 organised, groups of the fishes, it is hardly likely that we are 

 really presented here with the first examples of this great class. 

 On the contrary, whether the so-called " Conodonts" should 

 prove to be the teeth of fishes or not, we are justified in ex- 

 pecting that unequivocal remains of this group of animals will 

 still be found in the Lower Silurian. It is interesting, also, to 

 note that the first appearance of fishes the lowest class of 

 vertebrate animals so far as known to us at present, does not 

 take place until after all the great sub-kingdoms of invertebrates 

 have been long in existence ; and there is no reason for think- 

 ing that future discoveries will materially affect the relative 

 order of succession thus indicated. 



LITERATURE. 



From the vast and daily-increasing mass of Silurian literature, it is im- 

 possible to do more than select a small number of works which have a 

 classical and historical interest to the English-speaking geologist, or which 

 embody researches on special groups of Silurian animals anything like an 

 enumeration of all the works and papers on this subject being wholly out 

 of the question. Apart, therefore, from numerous and in many cases 

 extremely important memoirs, by various well-known observers, both at 

 home and abroad, the following are some of the more weighty works to 

 which the student may refer in investigating the physical characters and 

 succession of the Silurian strata and their fossil contents : 



(1) 'Sihiria.' Sir Roderick Murchison. 



(2) 'Geology of Russia in Europe.' Murchison (with M. de Verneuil 



and Count von Keyserling). 



(3) ' Bassia Silurien de Boheme Centrale.' Barrande. 



(4) ' Introduction to the Catalogue of British Palaeozoic Fossils in the 



Woodwardian Museum of Cambridge.' Sedgwick. 



(5) 'Die Urwelt Russlands.' Eicfrwald. 



(6) ' Report on the Geology of Londonderry, Tyrone,' &c. Portlock. 



(7) "Geology of North Wales" 'Mem. Geol. Survey of Great Britain,' 



vol. iii. Ramsay. 



(8) ' Geology of Canada,' 1863, Sir W. E. Logan ; and the ' Reports of 



Progress of the Geological Survey ' since 1863. 



(9) 'Memoirs of the Geological Survey of Great Britain.' 



(10) ' Reports of the Geological Surveys of the States of New York, 

 Illinois, Ohio, Iowa, Michigan, Vermont, Wisconsin, Minne- 

 sota,' &c. Bv Emmons, Hall, Worthen, Meek, Newberry, 

 Orton, Winchell, Dale Owen, &c. 



(n) ' Thesaurus Siluricus.' Bigsby. 



(12) 'British Palaeozoic Fossils.' M'Coy. 



(13) ' Synopsis of the Silurian Fossils of Ireland,' M'Coy. 



(14) " Appendix to the Geology of North Wales " 'Mem. Geol. Survey,' 



vol. iii. Sailer. 



